Is it possible to be too clean? Researchers say yes

The very tools we use to battle bacteria and viruses may actually end up 'training' our immune systems to attack allergens. NBC's Dr. Nancy Snyderman reports.

If you’ve been feeling guilty because you can’t keep your house spotless, stop.

As it turns out, allowing the odd germ to flourish here or there just might be saving your kid from a lifetime of allergies, Dr. Nancy Snyderman explained on "NBC Nightly News with Brian Williams" Monday.

It seems counterintuitive, but that’s exactly what the so-called "hygiene hypothesis" suggests. You can actually be too clean for your own good.

Scientists came up with the hypothesis as a way to explain the explosion of allergies and asthma in America’s youth. And what they discovered was intriguing, if a little disconcerting: kids who grow up in less tidy environments end up with a lower risk of developing sensitivities to benign substances, like pollen and dog dander.

A study released in June added to the growing mound of evidence that the too-clean-for-health hypothesis might be on track. That study, published in the Journal of Allergy and Clinical Immunology, found that Amish children who were raised on farms were less likely to develop allergies and asthma than their peers.

Why would exposure to dirt and microbes make a kid less sensitive to pollen and the like?

For one thing, it’s exposure to pathogens that allows the immune system to become fine-tuned as it learns to differentiate between harmful and harmless irritants.

“I believe that the immune system is like an army,” explains Dr. Samuel Friedlander, an allergist at University Hospitals Case Medical Center in Cleveland. “So, if the army doesn’t have something to fight like microbes, it’s going to fight things like allergens in many cases. People [who] live on farms are exposed to more microbes and as a result the immune system tries to fight those bugs and then, in turn, the body doesn’t have to fight allergens.”

Dr. Richard Gallo puts it a little differently. If you keep your environment too clean – by using too many bacterial soaps and hand sanitizers, for example – then your immune system becomes more sensitized to any irritant that comes its way.

“It’s a change in your allergic set point,” says Gallo, a professor and chief of dermatology at the University of California, San Diego. “So being too clean can lead you to have a high allergic set point that will overreact to the environment.”

Does that mean we can all throw out our mop buckets and soap? No, experts say. We still need to keep things clean, just not Bubble Boy antiseptic.

And there's an interesting side note: Some really intriguing animal studies have shown that you might be able to reset your immune system even after you’ve grown up by exposing yourself to certain types of bacteria.

“Some very recent studies that have been published in very excellent scientific journals have shown that with the introduction of specific bacteria in laboratory animals, you can completely reset their immune status and their capacity for certain allergic responses,” Gallo says.

And keep in mind, experts say, that some bacteria are fairly benign.

“So my advice is that some hygiene is good, too much is bad,” Gallo says. “In many cases you have to use common sense. You’re in a situation where you’re likely to be exposed to pathogens – germs that could cause disease – it’s a better idea to use sanitizers to remove them.

"But indiscriminate use - overusing hand sanitizers, anti-microbial soaps and so forth - is also going to be doing harm. So you have to balance the two.”